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<H2>equal_range()</H2>
<P><B>Module:</B>&nbsp;&nbsp;Standard C++ Library&nbsp;&nbsp;&nbsp;<B>Library:</B>&nbsp;&nbsp;<A HREF="2-9.html">Algorithms</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Complexity</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">See Also</A></LI>
<LI><A HREF="#sec8">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>Algorithm that finds the largest subrange in a range of values into which a given value can be inserted without violating the ordering of the values</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;algorithm&gt;

namespace std {
  template &lt;class ForwardIterator, class T&gt;
  pair&lt;ForwardIterator, ForwardIterator&gt;
  equal_range(ForwardIterator start, ForwardIterator finish,
              const T&amp; value);

  template &lt;class ForwardIterator, class T, class Compare&gt;
  pair&lt;ForwardIterator, ForwardIterator&gt;
  equal_range(ForwardIterator start, ForwardIterator finish,
              const T&amp; value, Compare comp);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>equal_range()</SAMP> algorithm performs a binary search on an ordered range to determine where the element <SAMP>value</SAMP> can be inserted without violating the range's ordering. The library includes two versions of the algorithm. The first version uses <SAMP>operator&lt;()</SAMP> to search for the valid insertion range, and assumes that the sequence was sorted using the same ordering. The second version allows you to specify a function object of type <SAMP>Compare</SAMP>, and assumes that <SAMP>Compare</SAMP> was the function used to sort the sequence. The function object must be a binary predicate. </P>
<P><SAMP>equal_range()</SAMP> returns a pair of iterators, <SAMP>i</SAMP> and <SAMP>j</SAMP>, that define a range containing elements equivalent to <SAMP>value</SAMP>, in other words, the first and last valid insertion points for <SAMP>value</SAMP>. If <SAMP>value</SAMP> is not an element in the container, <SAMP>i</SAMP> and <SAMP>j</SAMP> are equal. Otherwise, <SAMP>i</SAMP> points to the first element not "less" than <SAMP>value</SAMP>, and <SAMP>j</SAMP> points to the first element greater than value. In the second version, the ordering is defined by the comparison object. Formally, <SAMP>equal_range()</SAMP> returns a sub-range <SAMP>[i, j)</SAMP> such that <SAMP>value</SAMP> can be inserted at any iterator <SAMP>k</SAMP> within the range without violating the ordering. Depending upon the version of the algorithm used, <SAMP>k</SAMP> must satisfy one of the following conditions: </P>
<P><SAMP>!(*k &lt;  value)  &amp;&amp;  !(value  &lt;  *k)</SAMP></P>
<P> or </P>
<P><SAMP>comp(*k,value) == false &amp;&amp; comp(value, *k) == false</SAMP></P>
<P>The range <SAMP>[start,finish)</SAMP> is assumed to be sorted. Type <SAMP>T</SAMP> must be LessThanComparable.</P>
<A NAME="sec5"><H3>Complexity</H3></A>
<P><SAMP>equal_range()</SAMP> performs at most <SAMP>2 * log(finish - start) + 1</SAMP> comparisons.</P>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
// eqlrange.cpp
//

#include &lt;algorithm&gt;
#include &lt;functional&gt;
#include &lt;iostream&gt;
#include &lt;vector&gt;



int main ()
{
    // Typedef for convenience.
    typedef std::vector&lt;int, std::allocator&lt;int&gt; &gt; vector;

    vector::value_type arr[] = {
        0, 1, 2, 2, 3, 4, 2, 2, 2, 6, 7 
    };

    // Set up a vector.
    vector v1 (arr, arr + sizeof arr / sizeof *arr);

    // Try equal_range variants.
    std::pair&lt;vector::iterator, vector::iterator&gt; p1 =
        std::equal_range (v1.begin (), v1.end (), 3);

    std::pair&lt;vector::iterator, vector::iterator&gt; p2 =
        std::equal_range (v1.begin (), v1.end (), 2,
                     std::less&lt;vector::value_type&gt; ()); 

    // Output results.
    std::cout &lt;&lt; "\nThe equal range for 3 is: "
              &lt;&lt; "(" &lt;&lt; *p1.first &lt;&lt; " , " 
              &lt;&lt; *p1.second &lt;&lt; ")" &lt;&lt; std::endl;

    std::cout &lt;&lt; "\nThe equal range for 2 is: "
              &lt;&lt; "(" &lt;&lt; *p2.first &lt;&lt; " , " 
              &lt;&lt; *p2.second &lt;&lt; ")" &lt;&lt; std::endl; 

    return 0;
}


Program Output
</PRE></UL>
<UL><PRE>
The equal range for 3 is: (3 , 4)

The equal range for 2 is: (2 , 3)
</PRE></UL>
<A NAME="sec7"><H3>See Also</H3></A>
<P><B><I><A HREF="binary-function.html">binary_function</A></I></B>, <SAMP><A HREF="lower-bound.html">lower_bound()</A></SAMP>, <SAMP><A HREF="upper-bound.html">upper_bound()</A></SAMP></P>
<A NAME="sec8"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.3.3</I></P>

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